Phase Ib- same as Phase Ia except radiator intake is shorter, two small
intakes appear ahead of the main one.

Phase Ic- same as Phase Ib except the exhaust stack becomes shorter.

Phase IIa- entire hood below the radiator is the same width as the radiator
itself, radiator intakes are redesigned, the raised section on the radiator
disappears, a horizontal drip rail appears on the sides of the radiator,
short exhaust stack, small taper just ahead of the radiator, pipe chain guards
at right front corner.

Phase IIb- the taper just ahead of the radiator disappears, six equipment doors on the left side instead of eight.

Phase IIc- the intake screens become corrugated instead of flat, and project
slightly from the hood instead of being flush-mounted.